“Not Responding” sometime shows up in the main bar of an operating program when Windows finds that the program isn’t acting appropriately.  The precise reason is based on the certain program and the task you were involved in at that moment.

As Windows requests a program to perform a task such as stroking a key or ending a program and the program doesn’t obey this request within a specific period of time then the program is considered to be “Not Responding”.  If the program continues to be this way permanently this may be known as being “hung” or in other words “hung up” on something.

A bad or overburdened windows registry system frequently is the reason that software programs malfunction and display “not responding” error messages and additional errors that appear on your computer screen.

There are some solid reasons why you get the “Not Responding” error, for example, if the program being used is employed for making very long intensive calculations using up all resources on the Central Processing Unit (CPU), then the program might not respond in a time bound manner. To illustrate this point further,  supposedly a graphic program is being used on a large sized image in order to reduce the size of the image or to perform certain other functions and if during that process it happens that you make an attempt to shut down the window and no response is there for a few seconds then that means that the Windows program is not responding to the command of shut down; rather the command has been passed on to the Graphics program and that program is also not attending to the given command and thus ultimately leading you to a state of confusion.